The long term goal is to define central neural and hormonal mechanisms responsible for the regulation of arterial pressure. Although numerous studies point to a prominent relationship of the solitary nuclei and ventrolateral medulla with the rostral pons and paraventricular nucleus of the hypothalamus for cardiovascular control, the role of neurons in these areas in the processing of hemodynamic signals and in the reflex regulation of arterial pressure in response to changes in intravascular volume remains largely speculative. This study is designed to examine: 1. the processing of hemodynamic signals by neurons in the parabrachial nuclei of the pons and in the paraventricular nucleus of the hypothalamus of the rat using single neuron recording, 2. the role of neurons in the parabrachial nuclei, locus coeruleus, and paraventricular nuclei, in the reflex control of arterial pressure in response to hemorrhage or analogs of hemorrhage and in the basal control of arterial pressure in freely behaving rats, using electrolytic and neurotoxin lesions, 3. using neurotoxin lesions the efferent pathways responsible for cardiovascular changes induced by stimulation of neurons in the parabrachial nuclei, locus coeruleus, and paraventricular nuclei with excitatory amino acids. These studies should provide the information necessary to development a comprehensive description of some of the brain stem and hypothalamic systems responsible for control of arterial pressure.